Embodiments of the present invention relate generally to surface measurements of an eye and more particularly, to corneal topography or wavefront measurements of the eye based on estimation.
Known laser eye surgery procedures generally employ an ultraviolet or infrared laser to remove a microscopic layer of stromal tissue from the cornea of the eye. Examples of laser eye surgery procedures include photorefractive keratectomy (PRK), phototherapeutic keratectomy (PTK), laser assisted in situ keratomileusis (LASIK), laser epithelial keratomileusis (LASEK), and the like. A laser typically removes a selected shape of a corneal tissue, often to correct refractive errors of an eye. Ultraviolet laser ablation results in photodecomposition of a corneal tissue, but generally does not cause significant thermal damage to adjacent and underlying tissues of an eye. Irradiated molecules are broken into smaller volatile fragments photochemically, directly breaking intermolecular bonds.
Laser ablation procedures can remove a targeted amount of corneal stroma to change the corneal contour for varying purposes, such as for correcting myopia, hyperopia, astigmatism, and the like. Control over a distribution of ablation energy across a cornea may be provided by a variety of systems and methods, including use of ablatable masks, fixed and moveable apertures, controlled scanning systems, eye movement tracking mechanisms, and the like. In known systems, a laser beam often comprises a series of discrete pulses of laser light energy, with a total shape and amount of tissue removed being determined by a shape, size, location, and/or number of laser energy pulses impinging on the cornea. A variety of algorithms may be used to calculate the pattern of laser pulses used to reshape the cornea so as to correct a refractive error of an eye. Known systems make use of a variety of forms of lasers and laser energy to effect a correction, including infrared lasers, ultraviolet lasers, femtosecond lasers, wavelength multiplied solid-state lasers, and the like. Alternative vision correction techniques make use of radial incisions in a cornea, intraocular lenses, removable corneal support structures, and the like.
Known corneal correction treatment methods have generally been successful in correcting standard vision errors, such as myopia, hyperopia, astigmatism, and the like. By customizing an ablation pattern based on wavefront measurements, it has been possible to correct minor aberrations so as to reliably and repeatedly provide visual acuity greater than 20/20. Such detailed corrections benefit from an extremely accurate ablation of tissue.
Known methods for calculation of a customized ablation pattern using wavefront sensor data generally involves mathematically modeling a surface of the cornea using expansion series techniques. More specifically, Zernike polynomials have been employed to model the corneal surface and refractive aberrations of the eye. Coefficients of a Zernike polynomial are derived through known fitting techniques, and an optical correction procedure is then determined using a shape indicated by a mathematical series expansion model.
More recently, refractive correction treatments have considered combining corneal topography measurement data with wavefront measurements to determine the ablation pattern. Conventional corneal topography measurements are typically noisy and can include gaps in the measured field. Wavefront aberrometers and other in vivo ophthalmic measurement devices often face the same problem. The full image derived from such devices can be restored by decomposing available data into Zernike series or any other orthogonal basis functions. However, the accuracy of such decomposition, depending on the measurement noise level and the sample size of available data, needs to be evaluated. Oftentimes, there is a need to optimally combine several arbitrary sets of measurement data together with a priori information about the measured field.
For example, corneal or wavefront data acquired by medical diagnostics devices, such as the WaveScan® aberrometer by Abbott Medical Optics Inc. or the Atlas™ corneal topographer by Carl Zeiss Meditec, Inc., are typically converted to a two-dimensional field by known interpolation scheme or through decomposition of available data into Fourier or orthogonal polynomials with subsequent reconstructions of the two-dimensional field from those decompositions.
Hence, although current approaches provide benefits to patients in need thereof, there continues to be a need for improved ophthalmic measurement data techniques, particularly for refractive correction. Embodiments of the present invention provide solutions for at least some of these outstanding needs.